You can calculate your rank using
rank formula for jee mains is is (100 - your total score) X 869010 /100.100 (tel:869010100100) - your total percentile score is the percentage  of people ahead of you. 869010 (tel:869010) are the number of candidates appeared for Jan exam.If the number of candidates for April exam increased to 1200000 (tel:1200000) then your final rank shall be (100 - your total score) X 1200000/100 (tel:1200000100)
So your approximate general  rank will be 60270

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